1. Field of the Invention
The present invention relates to a poly(hydroxy ester ether) thermoplastic composition having barrier properties and to articles made from such polyesters and blends of such polyesters.
2. Background of the Invention
Because of their transparency, low permeability to oxygen, carbon dioxide, and water vapor, as well as low permeability to various products indigenous to foods, thermoplastic polyesters such as poly(ethylene terephthalate) (PET) and poly(ethylene naphthalate) (PEN) are used commercially in the packaging of various materials such as seasonings, carbonated beverages, detergents, cosmetics, and the like. While PET exhibits adequate barrier properties for packaging some materials, its oxygen barrier properties are inadequate for the packaging of more oxygen sensitive foodstuffs and beverages such as beer, wine, or low acid foods such as meats or vegetables.
Presently there is a strong interest in the packaging industry for protecting such oxygen sensitive foodstuffs in moldable thermoplastic materials where such materials have an oxygen transmission rate of less than about 15 cm.sup.3 -mil/100 in.sup.2 -24 hr-atm at 76% relative humidity.
U.S. Pat. No. 5,134,201 discloses a thermoplastic polymeric composition composed of a blend of: a) a linear, saturated polyester of aromatic diacids, such as PET; and b) a thermoplastic methylolpolyester which is miscible with component (a) and which has repeating units of: ##STR2## wherein each of R.sub.1 and R.sub.2 is individually a divalent organic moiety which is predominantly hydrocarbon, each R.sub.3 is individually hydrogen or lower alkyl, y is about 0.5, and x is a fraction from about 0.05 to about 0.4.
U.S. Pat. No. 5,780,582 discloses a hydroxy functional polyester oligomers that are useful as hot melt adhesives. The poly(hydroxy ester) and poly(hydroxy ester ether) oligomers are derived from hydroxy-functional aliphatic diacids and diglycidyl ethers.
U.S. Pat. No. 4,436,895 discloses a polyester resin composed of the reaction product of a diol containing up to about 8 carbon atoms and a diacid component which includes terephthalic acid and a second diacid selected from iminodiacetic acid, oxydiacetic acid, thiodiacetic acid, and mixtures thereof The second diacid is present in a concentration of about 1 to 50 mole percent, based upon the total amount of diacid. The polyester resin has an inherent viscosity of about 0.5 to 1.5. A preferred polyester is derived from ethylene glycol, terephthalic acid, and oxydiacetic acid. The containers are formed from the polyester have improved resistance to gas permeability.
European patent specification EP 0 542 972 and discloses a thermoplastic barrier polymer having aromatic ether moieties and amide moieties in the backbone chain and pendant hydroxyl moieties that is prepared by reacting one or more amide-containing bisphenols and an epihalohydrin.
While molded containers formed from polyethylene terephthalate have many desirable characteristics, there is a need in the art to provide improved polyester containers which will have a gas permeability, and specifically an oxygen permeability, which is lower than those of containers formed from the aforementioned polyesters and blends of polyesters. Containers from such improved materials would be much more versatile in their utilization and allow the containers to be used to package substances for which the polyethylene terephthalate containers may not be suitable.
In view of the limitations of the prior art, it would be desirable to provide a composition having improved barrier properties. It would further be desirable to provide a composition with improved compatibility which may be blended with polyesters, such as PET, and poly(hydroxy ester ethers) to provide compositions with improved barrier properties and not be subject to limitations found in immiscible blends.
It has now been found that containers which are formed from the specified composition of the present invention exhibit desirable physical properties, including improved gas barrier properties, which render them advantageous for use in packaging of oxygen sensitive foodstuffs.